1. Field of the Invention
The present invention relates generally to a broadband wireless communication system, and in particular, to an apparatus and method for allocating radio resources in a broadband wireless communication system by adaptively grouping the radio resources.
2. Description of the Related Art
Extensive research is being conducted to develop adaptive radio resource allocation schemes for efficiently using limited radio resources in a broadband wireless communication system. For example, a wireless communication system based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard allocates radio resources to user terminals using time-frequency resources, as illustrated in FIG. 1.
FIG. 1 is a diagram illustrating a conventional resource allocation architecture in a wireless communication system.
As illustrated in FIG. 1, the wireless communication system allocates radio resources using a location/size resource allocation scheme. For a DownLink (DL), the wireless communication system allocates radio resources in a two-dimensional fashion in consideration of time and frequency axes. For an UpLink (UL), the wireless communication system allocates radio resources according to resource lengths in a one-dimensional fashion in consideration of only the time axis (in a layered fashion along the frequency axis).
At this point, using a map, the wireless communication system provides each user terminal with radio resource allocation information (the size and start position of radio resources).
For the uplink, the map contains two-dimensional location/size resource allocation information including the length and the start point of the frequency axis and the length and the start point of the time axis. For the downlink, the map contains one-dimensional location/size resource allocation information including the length and the start point of the time axis.
As described above, the wireless communication system allocates radio resources using a two-dimensional resource allocation scheme and a one-dimensional resource allocation scheme. When the wireless communication system uses the two-dimensional resource allocation scheme, the wireless communication system allocates radio resources in consideration of both the time axis and the frequency axis, which increases the freedom of radio resource allocation for the respective user terminals. However, when the wireless communication system uses the two-dimensional resource allocation scheme, there is an increase in the size of a map for a transmission of resource allocation information to the respective user terminals.
When the wireless communication system uses the one-dimensional resource allocation scheme, the wireless communication system allocates radio resources in consideration of only the time axis, which reduces the map size. However, when the wireless communication system uses the one-dimensional resource allocation scheme, the start point of each burst is not fixed but changes for each frame.
When the wireless communication system uses the two-dimensional resource allocation scheme, the resource allocation information increases. When the wireless communication system uses the one-dimensional resource allocation scheme, the time point is not fixed. The wireless communication system may use a tree allocation scheme in order to solve the above problems.
FIG. 2 is a diagram illustrating a conventional tree allocation scheme in the wireless communication system.
When a tree allocation scheme is used as illustrated in FIG. 2, the wireless communication system constructs a tree of all radio resources using 2n-sized tree nodes. Thereafter, the wireless communication system allocates tree nodes in the tree according to the amount of radio resources that is needed by user terminals.
For example, when the maximum resource size is 24 (=16), the wireless communication system constructs a tree of all of the radio resources using 16, 8, 4 and 2-sized tree nodes. Thereafter, the wireless communication system allocates tree nodes according to the amount of radio resources that is needed by user terminals. If a user terminal needs 4 radio resources, the wireless communication system allocates a treed node 5 to the user terminal. In this case, the user terminal is actually allocated 9th through 12th radio resources.
As described above, the wireless communication system constructs a tree of all of the radio resources using 2n-sized tree nodes and allocates radio resources in units of the tree node. Therefore, when radio resource allocation information needs to be transmitted in a wireless communication system using the tree allocation scheme, the wireless communication system has only to provide tree node IDentifications (IDs) allocated to user terminals. Thus, when the maximum radio resource size is 2R, the wireless communication system needs only an (R+1)-bit address space for indicating radio resource allocation information. Accordingly, it is possible to reduce the size of a map for a transmission of resource allocation information.
In addition, when the wireless communication system uses the tree allocation scheme, the start position of radio resources is fixed and thus periodic resource allocation can be performed on the respective user terminals.
However, when the wireless communication system uses the tree allocation scheme, it allocates radio resources in units of the 2n-sized tree node, causing a waste of the radio resources i.e., because the size of allocated radio resources is fixed in units of the tree node, the wireless communication system may allocate more radio resources than are needed by user terminals. For example, when the wireless communication system uses the tree allocation scheme illustrated in FIG. 2, it allocates a 4 (=22)-sized tree node to a user terminal that needs 3 radio resources i.e., the wireless communication system wastes one radio resource. When a user terminal needs 9 radio resources, the wireless communication system allocates a 16 (=24)-sized tree node to the user terminal, i.e., the wireless communication system wastes 7 radio resources.
Moreover, when the wireless communication system uses the tree allocation scheme, the start position of allocable resources is very restrictive. Therefore, when the allocation and elimination of radio resources are repeated in the wireless communication system, there occurs a serious resource segmentation problem where a large-sized resource cannot be allocated due to the scattering of available radio resources.